Hot spot detection and protection methods for photovoltaic systems

Photovoltaic (PV) systems are becoming more prevalent as countries around the world focus on integrating renewable energy resources into their power grids. Also, there is a need for power grids to become more intelligent and adaptive. As a result, PV systems require additional functionality, such as the ability to monitor their operation for problems or faults and intelligently adapt the system as needed. This work focuses on adding detection and protection to PV systems for a temporary fault called hot spotting that occurs in series-connected PV cells. The present-day solution to mitigate hot spotting is the use of bypass diodes over subpanel PV strings. Simulation and experimental results show that bypass diodes are inadequate to prevent hot spotting, which leads to damage that permanently degrades the PV cell performance. Hot spotting can be detected by monitoring the ac small-signal characteristics of a PV string at various frequencies to measure the parallel capacitance and resistance of the string. When hot spotting occurs within a sting, both capacitance and resistance values increase by a measurable amount. An algorithm that dynamically measures the PV string impedance during normal operation is pursued as a low-cost hot spot detection approach. This hot spot detection algorithm can be integrated into a dc-dc converter that controls the PV string. For hot spot prevention, there are a few potential approaches to mitigate hot spot damage, but open-circuit protection is the only one that completely stops hot spotting. A protection device is developed that replaces the bypass diodes to provide both bypass and hot spot prevention capability. This hot spot prevention device was validated in experimental tests to stop the hot spotting within one minute after open-circuit protection is activated. Eventually, a combined solution of impedance-measurement-based hot spot detection coupled with open-circuit protection can be integrated into PV systems to eradicate hot spot damage and increase lifetime power output